Exploring Past and Future Drivers of Biogenic SOA

Atmospheric aerosols

aerosols

Small particles or droplets, such as wildfire smoke, volcanic gases, or salty sea spray, that float in the air. They are emitted by both natural events and human activities.

Source: NASA Global Climate Change Source

are the dominant contributor to uncertainty in global climate forcing. The accurate determination of radiative effects of aerosols relies critically on our ability to model and predict the loadings and properties of atmospheric aerosols, both in polluted and pristine (pre-industrial and remote) atmospheres. A major uncertainty is the contribution of biogenic secondary organic aerosol (SOA),

secondary organic aerosol (SOA)

Secondary Organic Aerosols (SOAs) are air pollutants emitted from natural and man-made sources. They are produced through a complex interaction of sunlight, volatile organic compounds from trees, plants, cars or industrial emissions, and other airborne chemicals.

Source: EPA Environmental Protection Agency Source

whose formation is highly dependent on reaction conditions. While research over the last 10-15 years has provided substantial insight into the underlying chemistry of SOA formation, the laboratory data needed for the accurate prediction of biogenic SOA, particularly under pristine (low-NOx) conditions, are largely lacking.

This proposed project, involving both experimental and modeling work, is aimed at gaining an improved understanding of biogenic SOA formation under pristine, low NOx conditions. Laboratory and modeling studies will focus on the role of RO2 isomerization (autoxidation) chemistry on SOA formation, as well as the temperature dependence of SOA chemistry; both are likely to be key drivers under global change, but have not been systematically studied in terms of their influence on global SOA levels. The specific objectives of this project are:

1.     To investigate and characterize the chemical formation of SOA from a range of biogenic precursors under conditions representative of both the pre-industrial era and present day.

2.     To investigate the sensitivity of biogenic SOA and the direct radiative effect (DRE) of biogenic SOA to global change from pre-industrial to future.

This project builds directly on the PIs’ previous work, including ARM-funded work on aerosol formation mechanisms. Laboratory studies involve chamber studies examining SOA formation from biogenic hydrocarbons, reacted under carefully-controlled conditions, spanning a range of RO2 chemical regimes (reaction with NO, reaction with HO2, or isomerization) and temperatures (12-40ºC). Key outputs from such studies are temperature-dependent RO2 isomerization rate constants (kisom), and SOA volatility distributions as a function of temperature and RO2 pathway, for all biogenic species studied; these parameters serve as the key inputs for the global modeling component of the project. Modeling work will characterize the global fate of biogenic RO2 and pathways for biogenic SOA formation using the Community Earth System Model

earth system model (ESM)

A model that simulates how chemistry, biology, and physical forces work together. These models are similar to, but much more comprehensive than, global climate models.

Source: U.S. Department of Energy Source

(CESM) and will be applicable to DOE's Energy Exascale Earth System Model (E3SM).

Energy Exascale Earth System Model (E3SM)

The Energy Exascale Earth System Model (E3SM) project includes Earth System Models, simulations, and predictions to investigate energy-relevant science using code optimized for DOE's advanced supercomputers.

Source: NVCL Web Page Source

Global model simulations will examine the evolution of RO2 chemistry and its effect on SOA formation, from the preindustrial to the present-day and into the future, as well as how expected changes in climate and emissions will affect global biogenic SOA in the future atmosphere. By developing and implementing descriptions of formation of SOA formation that better reflect our current understanding of the underlying chemistry, this project will improve the fidelity of our assessment of the global burden, and ultimately the climate effects, of biogenic SOA over time.